(1) Field of the Invention
The present invention relates to a tester and testing method for differential data drivers.
(2) Description of the Prior Art
FIG. 1 is a schematic block diagram showing a conventional differential data driver tester. FIG. 2 is a waveform chart showing crossover voltage waveforms of a differential data driver. As shown in FIG. 1, in a differential data driver 1, data input from a data input terminal 13 is supplied to a (D+)data output driver 11 and (Dxe2x88x92)data output driver 12. An enable signal is supplied from a driver output enable signal terminal 14 so as to set (D+)data output driver 11 and (Dxe2x88x92)data output driver 12 into data output states, whereby differential signals via (D+)data output line 15 and (Dxe2x88x92)data output line 16 are transferred to a (D+)data input terminal 18 and (Dxe2x88x92)data input terminal 19 of a tester 17, respectively. For this differential data driver 1 to transfer differential data, it is necessary that as shown in FIG. 2, the crossover voltage(VCRS), designated by 25, between output signal 21 transferred from (D+)data output driver 11 and output signal 22 transferred from (Dxe2x88x92)data output driver 12, should fall within a reference voltage range, specified by a crossover upper limit voltage(VOH) 23 and crossover lower limit voltage(VOL) 24.
Conventionally, the test on the differential signals in differential data driver 1 has been made in the following manner. Time(t1) 210 at which (Dxe2x88x92)data output signal 22 has reached a point 28 or crossover lower limit voltage(VOL) 24 and time(t2) 211 at which (D+)data output signal 21 has reached a point 26 or crossover upper limit voltage(VOH) 23 are measured from a certain time t0. Similarly, time(t3) 212 at which (Dxe2x88x92)data output signal 22 has reached a point 27 or crossover upper limit voltage(VOH) 23 and time(t4) 213 at which (D+)data output signal 21 has reached a point 29 or crossover lower limit voltage(VOL) 24 are measured. In tester 17, when these measured values satisfy t1 less than t4 and t2 less than t3, crossover voltage (VCRS) 25 are determined to fall between crossover upper limit voltage (VOH) 23 and crossover lower limit voltage(VOL) 24, and hence the measured differential signals are determined to meet the specifications.
However, in the above testing method, when it is to be examined whether the crossover voltage (VCRS) 25 falls within the reference voltage range, time and voltage measurements need to be made at, at least, four points. This makes the tester 17 configuration complex.
In tester 17, the differential signal transferred via a (D+)data output line 15 from (D+)data output driver 11 of differential data driver 1 and the differential signal transferred via a (Dxe2x88x92)data output line 16 from (Dxe2x88x92)data output driver 12 are tested separately. Therefore, the problem of channel-to-channel skew occurs upon measurement. Thus, in the conventional technique, the precise measurement of the differential signals from differential data driver 1 has been difficult to be made.
The present invention has been devised in order to solve the above problems and it is therefore an object of the present invention to provide a tester circuit and testing method for a differential data driver which has a simple configuration and yet can test the differential signals with a high precision.
As the means for achieving the above object, the present invention is configured as follows:
In accordance with the first aspect of the present invention, a tester for differential data drivers is characterized in that the acceptability of two differential signals from two data output terminals of a differential data driver is determined based on the sum of the voltages of the two signals.
In accordance with the second aspect of the present invention, the tester for differential data drivers having the above first feature is characterized in that a pair of resistors, having substantially equivalent resistance are arranged in series so that the two data output terminals of the differential data driver are connected to the ends of the series of resistors, whereby the sum of the potentials of the two signals are detected by resistively dividing the potentials of the two output signals from the differential data driver.
In accordance with the third aspect of the present invention, the tester for differential data drivers having the above second feature is characterized in that a switching device is arranged at each end of the series of resistors.
In accordance with the fourth aspect of the present invention, the tester for differential data drivers having the above third feature is characterized in that the switching devices are opened when tests other than the acceptability judgement as to the differential signals are implemented.
In accordance with the fifth aspect of the present invention, a testing method for differential data drivers is characterized in that the acceptability of two differential signals from two data output terminals of a differential data driver is determined based on the sum of the voltages of the two signals.
In the configuration of the present invention, the tester for differential data drivers determines the acceptability of the differential signals from a differential data driver, based on the sum of the voltages of the two signals output from two data output terminals of the differential data driver. Accordingly, it is possible to make a judgement as to the acceptability of the differential signals without measuring any elapsed time, hence simplify the tester configuration. Further, since the sum of the voltages of the (D+)data output signal and (Dxe2x88x92)data output signal is examined, the tester can make the test using a single channel. Accordingly, it is possible to implement high-precision measurement without being affected by channel-to-channel skew.
In the configuration of the present invention, the tester for differential data drivers includes a series of two resistors, having substantially equivalent resistance and arranged in such a manner that the two data output terminals of the differential data driver are connected to the ends of the series of resistors, whereby the sum of the potentials of the two signals is detected by resistively dividing the potentials of the two output signals from the differential data driver. Therefore, the configuration of the tester can be made simple. Further, the combined signal of the (D+)data output signal and (Dxe2x88x92)data output signal is used for testing, so that the test can be implemented using a single channel of the tester, which makes high-precision measurement free from influence of channel-to-channel skew possible.
In the tester for differential data drivers thus configured in the present invention, a switching device is arranged at each end of the series of resistors. Therefore, tests for other than the acceptability judgment as to the differential signals can be implemented excluding the influence of the series of resistors.
In the tester for differential data drivers thus configured in the present invention, the switching devices are opened when tests other than the acceptability judgement as to the differential signals are implemented. Accordingly, the series of resistors can be used appropriately depending on the purpose of the test in the tester.
In the configuration of the present invention, the acceptability of the differential signals from a differential data driver is determined based on the sum of the voltages of the two signals output from two data output terminals of the differential data driver. Therefore, the acceptability judgement as to the differential signals can be made without measuring any elapsed time, thus making it possible to test differential data drivers easily.